Wettability is an important phenomenon significantly impacting fluid distribution and dynamics in porous media. Specifically, in order to find solutions to multiple research and engineering problems in the petroleum industry rock characteristic properties need to be determined, including mineral composition, pore volume structure, and pore surface wettability. These are the key properties for understanding oil and gas formations and simulating fluid flow properties: phase permeability, displacement factor, etc. Changes in free surface energy associated with rock/fluid interface result in heat emission or absorption. The heat effect value is a function of specific surface and pore volume wettability. In endothermic processes, such as most phase transitions, heat is absorbed.
The conventional approach to core wettability determination is the Amott method and its modifications (See, for instance, J. C. Trantham, R. L. Clampitt, Determination of Oil Saturation After Waterflooding in an Oil-Wet Reservoir—The North Burbank Unit, Tract 97 Project, JPT, 491-500 (1977)). The Amott method is based on the fact that a wetting fluid can spontaneously saturate a rock core displacing a non-wetting fluid. The main disadvantage of the Amott method is a big error in core analysis both of neutral wettability samples and small-sized samples (less than 1 inch).
Nuclear Magnetic Resonance (NMR) is also a core analysis method used to determine pore size distribution (U.S. Pat. No. 4,291,271). The method is based on determining fluid distribution in the core and could only give indirect evidence of rock sample wettability.
The results of calorimetric studies have been increasingly used lately in determining properties of porous materials. Calorimetric methods can be used to study solid/liquid interfaces. The Differential Scanning calorimetry (DSC) can measure heat effects caused by phase transitions, changes in the system inner energy, and chemical reactions as a function of temperature. In DSC a difference between heat flow to a sample and a reference at the same temperature is recorded as a function of temperature. The reference may be an inert material such as alumina, or just an empty cell (International Standard ISO 11357-1, Plastics—Differential Scanning calorimetry (DSC), First edition 1997 Apr. 15). The heat effect may be either positive or negative. In most phase transitions, heat is absorbed. Therefore heat flow to the sample is higher or than that to the reference. Hence, the difference is positive.